1. Field of the invention
This invention is directed to a control device for an automatic transmission, which has plural and non-continuous gear stages, is controlled based on the information regarding the road condition of the route that the vehicle follows. This information is output by a route information detection device.
2. Related Art
Generally, the gear stage of an automatic transmission for a vehicle is automatically controlled by the driving condition of the vehicle, which is detected by various sensors. Although if sensors are used to detect the vehicle driving condition, they can only detect the change of the vehicle driving condition when the vehicle encounters an actual change in road conditions. So, if sensors are used, the driving force is changed by shifting the gear stages after detection of an actual change in the driving condition, which sometimes reduces the drivability and performance of the vehicle. Recently, it has become possible for a route information detection system, for example, a navigation system, to detect in advance information regarding the road condition, on which the vehicle travels, and this information is used to control shifting of the gear stages of an automatic transmission before the road conditions actually change. An example of a vehicle control system is disclosed in Japanese Patent Laid Open Publication No. HEI 7-306998.
In the above mentioned patent, the vehicle control system has a digital map, which stores information on a road map, navigation system, which calculates location of the vehicle on the map, a wheel sensor, which detects the vehicle speed, a predict system, which predicts the route that the vehicle will follow, a driving skills determining system, which determine the driver's skills, an appropriate speed calculating system, which calculates an appropriate speed for the driver based on his driving skills, a comparison system, which compares the calculated appropriate speed and the actual running speed, a vehicle acceleration calculation system that calculates the acceleration that the vehicle should take to make the vehicle travel at said appropriate speed by taking into account the information from the comparison system, continuously variable transmission (CVT), and a transmission control system, which controls a speed ratio of the CVT based on the calculated vehicle acceleration. The above mentioned system takes the following steps when the vehicle road conditions where require deceleration, for example, to enable to go through a curve safely. First of all, the vehicle control system judges whether the driver will be able to through the curve smoothly through the curve at the present speed, the appropriate speed for going smoothly through the curve is calculated. Second of all, the speed plan is determined to decrease the vehicle speed from the present speed to the appropriate speed for going through the curve, and the target speed is determined. Taking into consideration the driver's skills, the vehicle deceleration is calculated to make the present vehicle speed the target speed. The maximum of this deceleration is set so the driver may not feel the deceleration. Consequently, without making the passengers uncomfortable, the vehicle decreases its speed to the appropriate speed for going through the curve before the vehicle reaches the curve, thereby enabling the vehicle to go smoothly through the curve.
Regarding the automatically controlled transmission, in addition to the continuously variable transmission (CVT), there is so a called automatic transmission which has plural and non continuous gear stages, consisting of the gear mechanisms and frictional engagement units. The gear stages are non continuous gear ratios, the gear stages are set by engaging one frictional engagement unit and disengaging another frictional engagement unit. When the gear stage of the automatic transmission changed, the frictional engagement units will engage or disengage, which causes shift shock during a shift change.
A vehicle, that has an automatic transmission, with non continuous gear stages, to go through a curve smoothly, should be controlled by decreasing its speed before the curve. It is also desirable to avoid changing the speed ratio during the curve. Although for a vehicle that has an automatic transmission, if the gear stage is changed from a higher stage to a lower stage to decrease the vehicle speed, it is possible that more than one shift changing will continuously occur, and consequently the shift shock of the gear shift changing will occur as well. That's why if the above mentioned invention is applied the same to a vehicle that has automatic transmission, it is impossible to prevent the occurrence of the shock of the speed changing.